In the current illuminating devices, especially in the large-power LED illuminating devices, most of the total thermal resistance of the illuminating device is the thermal resistance of the circuit board. Taking the conventional metal-based circuit board (MCPCB) as an example, heat generated by LED chips that can be regarded as heat sources during operation must be transferred to the base by passing through an electric-conducting layer and an insulating layer that are arranged in sequence on a surface of the metal base, such as on an aluminum base. Since the insulating layer is usually made from polymer, its thermal conductivity is quite low. This leads to relatively big thermal resistance between the LED chips and the metal base. Taking a relatively new ceramic-based circuit board (ceramic PCB) as an example, though heat generated by the LED chips that also can be regarded as heat sources during operation can be transferred to the ceramic base just by passing through an electric-conducting layer arranged on a surface of the ceramic base, due to the restrictions of ceramic, the ceramic base has relatively low thermal conductivity compared with the metal base, such as aluminum base, thus, the whole illuminating device still has high thermal resistance. Moreover, such ceramic-based circuit board is also easily broken or damaged and has a relatively big deadweight.